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October 2010

Vol. 15, No. 42 Week of October 17, 2010

Cook Inlet beluga whale count up in 2010

NMFS annual survey counts 19 more animals than in 2009 but agency says population trend heading downward, perhaps to extinction

Alan Bailey

Petroleum News

Last year it was 321 and this year it’s 340. But despite this small apparent increase in the Cook Inlet beluga whale population, announced by the National Marine Fisheries Service on Oct. 8, a vigorous debate continues over whether that population is declining, or whether it is starting a slow recovery from a precipitous drop in the 1990s.

The latest population estimate of 340 comes from a NMFS 2010 aerial survey, the latest of a series of surveys conducted each June, in which NMFS scientists overfly most of the upper Cook Inlet, Turnagain Arm and Knik Arm, counting beluga whales and shooting video images of whale pods for later analysis and more precise whale counting.

But although NMFS has confirmed a small increase in the population count this year, the agency is sticking with its view that the whale population is continuing a slow decline.

“Analysis over the past decade shows a gradual downward population trend of 1.1 percent,” NMFS said when announcing the 2010 survey result.

Endangered listing

And population trends matter, given the October 2008 NMFS decision to list the Cook Inlet beluga whales as endangered, a decision that has caused great concern about potential impacts on activities ranging from oil and gas development to wastewater treatment in and around the inlet.

In December 2009, NMFS announced its intent to designate 3,016 square miles, primarily encompassing the entire upper Cook Inlet, as beluga whale critical habitat, a proposal that created further angst for businesses and local governments with interests in the inlet. NMFS now says that it will issue its final ruling on the critical habitat on Oct. 22.

The essential problem with using the annual whale counts to establish a population trend is that the characteristics of the inferred trend depend on which years are included in the trend analysis. At a beluga whale science conference in Anchorage on Oct. 10, Rod Hobbs, leader of the beluga project at the national marine mammal laboratory of the National Atmospheric and Oceanic Administration, said that the agency’s trend estimate comes from data for the years 2001 to 2010, the rationale being that beluga whale subsistence hunting, thought to be the main culprit in a major population drop in the 1990s, had all but ended in 1999 following the introduction of new hunting regulations.

“Since then … the abundance has gone up and down, but for the most part has stayed between 300 and 400 animals,” Hobbs said.

Population recovering

Jason Brune, executive director of the Resource Development Council, has questioned the NMFS trend analysis and has particularly latched onto the survey data for 2005, the year when the estimated population dropped to a minimum of 278. Brune has quoted the work of Beluga whale specialist L.K. Litzky, who published a paper saying that it would take about six years for the beluga population to start to recover from the overharvesting of the whales in the 1990s.

That 2005 low point in the estimated population is consistent with Litzky’s findings, Brune has said. And then, a trend line from 2005 to the present shows a slow population recovery, not a decline, he has said.

At the Anchorage conference, in response to Brune’s critique, Hobbs said that the Litzky was using an idealized population model, while the predictions of the NMFS model are consistent with the 10-year decline trend. Besides, picking the lowest of the annual population counts as the starting point for a population trend will automatically result in an upward slope in the trend, he said.

Model predictions

The NMFS population model that Hobbs referred to uses the annual population estimates combined with a number of parameters, such as whale reproduction rates and estimates of the number of whales that the Cook Inlet could in principle support, to predict future whale populations and thus assess the chances of the whales surviving. In 2008, at the time of the beluga whale listing decision, the model indicated a 26 percent probability of extinction of the whales within 100 years, a probability greatly in excess of the 1 percent probability criterion that triggers an endangered species classification.

And at the Anchorage conference, Hobbs showed model projections 300 years into the future, with an analysis of the data indicating a 70 percent probability that the population is declining. This result matches the 10-year decline trend that NMFS has inferred from the annual population counts.

However, Doug Vincent-Lang, special assistant with the Alaska Department of Fish and Game, questions the NMFS model results. On Oct. 13 Vincent-Lang told Petroleum News that he views 300-year population projections on the back of a few years of actual population data as extremely suspect.

“A model is only as good as the assumptions that are built into it,” Vincent-Lang said. “… Trying to model something into the distant future using assumptions based on your current understanding of that population is probably not that valid.”

Model sensitivity

In particular, the model results are sensitive to the values used for the Cook Inlet carrying capacity (that is, the number of whales that the Cook Inlet should be able to support), Vincent-Lang said. And Fish and Game views 650, the size of the whale population that NMFS had estimated in the 1990s at the start of its annual surveys, as more realistic than the figure of 1,300 that NMFS uses, he said. In addition Fish and Game has found that predictions of whale extinction, especially after 50 years into the future, are highly dependent on estimates of future deaths from whale strandings.

Vincent-Lang said that Fish and Game had run the same model as the one that NMFS uses, but had projected the data forward for just 50 years and had come up with less than a 1 percent probability of extinction for the whales.

In response to Vincent-Lang’s comments, Hobbs told Petroleum News that he agrees that projecting whale populations 300 years into the future is questionable, but that the 300-year timeframe represents the running of the population model to completion. In fact, NMFS also runs the model over 50- and 100-year time periods, with 100 years being a more useful management horizon, he said.

However, Hobbs did not agree that the model results are especially sensitive to estimates of the Cook Inlet beluga whale carrying capacity.

“We looked at that and it makes a small difference, not a large difference,” Hobbs said.

Random events

Hobbs did agree that the population model predictions are sensitive to estimates of future whale deaths from random events such as whale strandings and predation by killer whales. Random whale deaths in excess of some threshold value that relates to the whale population size can push the population towards extinction.

At the current population level, just five beluga whale deaths in a year from killer whale predation, for example, could tip the beluga whale population into an irrecoverable decline, Hobbs said. Actual killings are thought to be about one per year, but could be higher, he said.






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